Summary: The genetic algorithm method has been utilized with a thermomechanical model to determine an optimum welding sequence. The thermomechanical model developed for this purpose predicts residual stress and distortion in thin plates. The thermal history of the plate is computed using a transient two-dimensional finite element model which serves as an input to the mechanical analysis. The mechanical response of the plate is estimated through a thermoelastic-viscoplastic finite element model. The proposed model is verified by comparison with experimental data where available. By choosing the appropriate objective function for the considered case, an optimum welding sequence is determined by a genetic algorithm.